In the oil and gas industry, following drilling of a vertical or horizontal wellbore into a formation for the production of oil or gas therethrough, the wellbore is typically cased and cemented to line the length of the wellbore to ensure safe control of production of fluids therethrough, to prevent water from entering the wellbore and to keep the formation from “sloughing” or “bridging” into the wellbore.
It is well known that during the running-in of the casing, particularly the production casing, the casing may encounter obstructions in the wellbore, such as created by sloughing of the wellbore wall into the open hole or as a result of the casing pushing debris ahead of the bottom end of the casing along the open hole until it forms a bridge. Such obstructions prevent the advance of the casing and require the open hole to be cleared in order to advance the casing to the bottom of the hole. This is particularly problematic in horizontal wellbores and in sandy formations.
Should the casing string becoming sufficiently engaged in the obstruction, differential sticking may occur, making advancing the casing into the wellbore or removal of the casing from the wellbore extremely difficult.
While casing strings may be rotated to assist with moving past or through an obstruction, high torque created by trying to rotate a long string of casing may result in significant damage to the threads between casing joints and may cause centralizers and the like to drag and ream into the wellbore. Rotation of casing may be an option, albeit fraught with problems, in a vertical wellbore, however rotation of casing in a horizontal wellbore is extremely difficult, if not impossible.
In U.S. Pat. No. 8,973,682, the subject matter of which is fully incorporated by reference herein, Applicant has provided a tool that can clear obstructions within wellbores without the need for rotating the casing string, substantially reducing problems associated with rotating the casing string, including but not limited to torque build along the casing string.
Further, in cased or lined wells, sand and debris continues to be an issue. Obstructions and accumulations of debris can be formed therein. Workover operations are performed to clean the cased wellbore and remove debris therefrom. Workover tools are known in the industry as are chemicals and other means of removing debris, including but not limited to sand, waxes and other debris.
In sandy environments, it is known to use nitrogen gas which is pumped into the wellbore to cause debris, such as from an obstruction, to be removed through the annulus between the casing and the nitrogen delivery tool. The use of nitrogen gas can be prohibitively expensive.
Further, mechanical bailers are also known. The bailer is generally a chamber which is lowered into the wellbore for lifting debris therefrom. Conventional bailers typically comprise a reciprocating pump assembly having a chamber for storage of debris therein. The conventional bailers however utilize hexagonal mandrels in the reciprocating pump which cannot be rotated. The inability to rotate is problematic particularly in horizontal wellbores.
Ideally, what is required is a relatively simple and inexpensive apparatus which can perform the function of Applicant's obstruction-clearing tool and the function of a known reciprocating pump.